Method of printing on transparent flexible foil material



May 27, 1941. H. HILLE METHOD OF PRINTING 0N TRANSPARENT FLEXIBLE FOILMATERIAL Filed July 2, 1938 /n Mentor I -HE/N/2/CH H/LLE AttorneysPatented May 21, 1941 METHOD OF PRINTING N TRANSPARENT FLEXIBLE FOILMATERIAL Heinrich Hille, Berlin, Germany, assignor to TransartAktiebolag, Gothenburg, Sweden, a corporation of Sweden Application July2, 1938, Serial No. 217,128 In Germany July 5, 1937 9 Claims.

This invention relates to the printing on sheets, webs or foils of thinflexible transparent ma-- terial, more particular of cellulose film ortransparent cellulosic materials such as those known on the marketunder, the trade names of Zellglas, Ultraphane, Cellophane, "Kodapackand the like, in the case of which, accurate register plays a mostimportant part. In the case of materials of the above-mentioned type,particularly of acetate foils, such register is much more difiicult toobtain than with paper, because the stretching of such foils during theprinting operation plays a not altogether unimportant part as comparedwith the case of paper. When printing on such transparent foils, a greatdeal depends on maintaining in accurate registenthe position of theprinted image, because when printing on both sides of the sheets, theimageon one side must be in perfect register with that on the otherside; on this is based the so-called Transart process. In ordinaryrotary printing machines, the transport of the web of material iseffected substantially through the printing units themselves and bymeans of the spindles mounted on and driven by the machine. Whenprinting on transparent cellulosic material, more particular oncellulose acetate stock, as Zellglas or like material, this guidingthrough the printing units is rendered even more difficult for thereason that the pressure applied by the pressure exerting means of theprinting units finds its limitation in the comparatively light coatingwith a plurality of superposed layers, such as those required with theTransart" process, and for which layers it is first necessary to providea suitable supporting and adhering base for the colours to be printedfor the time being, and for which no provision has to be made whenprinting with printing inks on paper capable in itself of easilyabsorbing them. This is precisely why the register question is twice asimportant for the prevention of ground edges.

A further difficulty resides in the fact that when using rotary printingmachines with a plurality of successively aligned printing units, andmore especially when they are of different types (such as letterpressprinting units, photogravure printing units and in some instancesaniline printing units) the tension strain of the web to be printed onby the different printing units is altogether different. Consequently,in the case off-combined letterpress and photogravure printii'lE, forexample, there is present with a material having a greater extensibilitythan paper an increasing non-registration of the top surface in relationto the bottom surface. While letter press printing units hold the web tothe size of the image to be printed, the guiding of the web,

of material when perfecting by printing the opposite side is effected,for instance, in photogravure units, over the whole width of theprinting cylinder. Even if the registration of the colours amongstthemselves, both in the letterpress printing units per se and also inthe photogravure sections per se were-brought about, there occursthrough the described differential strains of Zellglas or as the casemay be, acetate webs in the different printing units of the machine,variations leading to the defects alluded to, more especially when thetop side is to be printed by means of photogravure cylinders forexample, and the underside by means of letterpress cylinders.

In order to overcome these disadvantages, the

invention aims at printing on transparent cellulose material, moreparticular on cellulose acetate material of the above mentioned kind, e.g. the material known under the trade names Ultraphane, Zellglas or thelike in a stretched condition. For this purpose the tension of thestretched sheet or web may suitably be so calculated that during theprinting operation, no substantial additional stretching can take placeby the action of the printing mechanisms.

In the carrying out of the process, the printing units and the drivenspindles do not therefore take an essential part in the conveyance ofthe web. 0n the contrary, the transport may suitably be carried out by apowerful tension shaft which is provided in front of the cuttingcylinder and which pulls the web without any slipping under thenecessary amount of tension from the correspondingly braked materialreel. The pressure applied by the printing units themselves, cantherefore exert no unwanted stretching action on the material, as thelatter, from the first photogravure impression, for example, up to thelast letterpress impression will be pulled along uniformly and undersuch powerful tension through the machine, that deviations in theimpression pressures prevailing in the different printing units willhave no influence on the material itself.

In other words, the invention is based upon the following factsdiscovered by the inventor: With increasing load of the cellulosicmaterial foil its stretching at first gradually increases. Before itreaches the tearing point, however, a

. stage is reached where the extended material has on the onehandadequate solidity to withstand all the strains occurring in the courseof operation, and on the other hand to bring about no further additionaldetrimental extension or stretching of the material by the additionalstretching strains occurring in the different printing mechanisms.

If a cellulosic material foil extended in this manner is pulled throughthe machine, the printing units merely act as intermediate stations butnot as elements takingan important part in the guiding of the web. Thetension of the web is therefore perfectly uniform in all the machineparts from the braked material reel to the pulling spindle. The registerand the guiding are therefore also safeguarded when the pressure of thepressure exerting-means of the printing mechanism which no longer takesan active part in the transport, is comparatively small as desirable forthe above-mentioned reasons in the case of the Transart process forexample.

In order to ensure that the whole web will be kept continuously taut, itis necessary for the pulling spindle located between the last printingunit and the cutting cylinder to bear on the web with such a highpressing force, that notwithstanding the smooth surface no slipping willoccur. Consequently, this spindle may suitably be fitted with anespecially good gripping surface by using for instance one or moreroller bodies composed alternately of adjacently located cloth and indiarubber discs. It is advisable to have the roller bodies travel onunprinted parts of the material and it has been proved to be sufficientto grip the material adjacent the edges thereof.

The tension to be applied under which printing takes place, mustnaturally be adapted to prevailing operative conditions. Thus thesmaller the pressure applied by the pressure exerting means of theprinting units, the smaller can be the operative tension given to thefoil, and inversely as the pressure applied by the pressure exertingmeans of the printing units rises, so must the preliminary tension alsobe increased. The operative tension is obviously also dependent on thecharacter of the foil material used for the time being. 7

An attempt has been made to give in the following example, the tensionratios resulting during the printing of a cellulosic sheet materialknown commercially under the name of Ultraphan G No. 60. If a web ofthis material is printed in a machine equipped with a plurality ofsuccessively aligned printing units of different types, such as thoseillustrated in the drawing, the pulling tension preferably adopted forthe purpose of ensuring perfect register is so great, that a paper 60grams/m in weight would no longer be able to withstand the strain, butwould tear. The acetate foil pulled down from the braked reel and whichmoreover already possesses according to the supplying firm (Lonza Werkein Weil) a certain initial stretching of the magnitude of 1%, is oncemore extended by a powerful pulling spindle by about 1% in thelongitudinal direction and is printed in this stretched condition,whereby absolutely perfect register is obtained. By slackening thetension, that is, after leaving the machine, the stretching broughtabout by the pulling spindle substantially disappears, owing to theelasticity of the material. It is evident that, in this case, theappropriate tension for printing lies in the neighbourhood of the limitof elasticity. For, when reaching this value some considerable forcemust be exerted in order to provoke further stretch- -ing, which forcebeing obviously so large, in comparison with that exerted upon the webin the course of printing in the printing mechanisms, that the latterforces will no longer detrimentally make their appearance. Whenexercising the above large force the limit of the elasticity will soonbe exceeded. If the same material is stretched considerably more, sayfrom 3% to 5%, the stretched material, after the pulling is slackened,no longer retums,.whereas a rupture will only occur with a considerablyhigher stretching, namely an expansion of over 20% in length,corresponding to a pull of about 750 kilos per square centimetre.

One constructional form of the invention will now be described, byreference to the accompanying diagrammatic drawing. The reel of materialI is equipped with an adjustable brake 2, for example a band brake withan adjustable clamp lock 2a on one side of the band brake. In theconstruction illustrated by way of example, the machine is made up oftwo photogravure printing units 3 and I for printing on one side of theweb, two further photogravure printing units 5 and 6 for printing on theopposite side and four letterpress units 1 to H! for printing again onthe first side of the web. Before the machine is started up, the webfrom the reel is guided, over the usual guiding and conveying rollers,through the printing units 3 to III, which are preliminarily set toinoperative position and tripped (released from pressure). Then the webis guided through the bite formed by a pulling spindle H and acooperating pressure roller strongly urging the web without any slipagainst the positively driven pulling spindle, whence the web is fed tothe usual cutting cylinder [2. The pulling spindle is driven at aperipheral speed appropriate to ,the necessary operative stretching ofthe web which speed is therefore greater than that of the reel ofmaterial, whereas the form or, as the case may be, the copper cylinders,located in between, are all driven with the same normal operative speed.After the whole of the length of the web has been stretched to the aboveindicated degree by tightening the pulling spindle, the respectiveimpression cylinders or, as the case may be, pressing mechanisms, areadjusted, and the printing of the web is then effected continuously inthe usual man ner. The cutting cylinder cuts the printed web intosheets, which are delivered in the known manner.

The illustration in the drawing is only intended to explain theprinciple of the invention, which is not restricted to theconstructional form shown. For instance, between the reel of material I,and the photogravure printing unit 3, a further photogravure printingunit could be arranged.

All rollers engaging the web, i. e. the pulling spindle II, and allrollers cooperating with the web in the printing units, arecooperatively connected with each other and are positively driven bygears with the same circumferential speed. The web reel lis notpower-driven and is subjected to a braking action to such a degree thatthe circumferential speed of said reel is smaller than thecircumferential speed of the other rollers an amount corresponding tothe stretching effect exerted on the web by the pull of the spindle Inother words, the reactionary pull exerted on the web by the web reel 1against the action of the pull spindle II is, by suitable adjustment ofthe brake 2 rendered so powerful that the forces exerted on the web bythe printing units appear negligible compared therewith and cannotproduce any appreciable additional strain in the web which would affectthe accuracy of the register. The adjustment of the brake is to beadapted to the material printed upon, so that for instance thesubstitution of a material of other qualities (e. g. in respect ofelasticity) for the material used previously requires a correspondingchange in the adjustment of the brake to compensate the changes in thequalities or reactions of the material relative to the stressesexercised. The stress produced in the material is always many timeslarger than the stressesexercised on the material by the printing units,so that said last-named stresses do not make themselves noticeable anddo not detrimentally afiect the register.

In the Patent No. 1,867,405 to Irving Gurwick issued on July 12, 1932,it has been proposed prior to the present invention to print ontransparent sheets of a cellulose material and to pull the web for thispurpose from the supply roller by a feed or drawing roller firmlypressed upon the web and rotating at the same peripheral speed as theprinting cylinders. In this prior process the printing members engagedthe web at so slight a pressure as to avoid any participation in thefeed of the web, the feed being efiected independently of the printingmembers and solely by the feed roller. Experience has shown, however,that the mere tautening of the web in this manner is not sufficient toobtain a true register and that particularly wave formation in the webcannot be avoided. If considerable waves are formed, the feed rollermust be temporarily disengaged from the web.

I have discovered that I can obtain an accurate register in the printingoperation by the above described invention in which the web is not onlykept taut and fed past the printing rollers in this condition but inwhich the web is fed through the printing units in stretched extendedcondition. In this condition no waves or corrugations will be formed andwhile the permissible pressure of engagement of the printing. rollerwith the web was limited in the prior process, I may adjust the printingpressure to any desired suitable degree which is not subject to thehmitations present in the prior process. The only requirement to beobserved is that of such an extension of the web thatthe stress set uptherein is many times larger than the forces liable to be exerted on theweb by the printing units and tending to produce an additional straintherein. If I use a drawing spindle pulling the web from a braked supplyroller and thus feeding the web through the printing units which do notparticipate in the feeding operation, the braking force exerted on thesupply roller must be so chosen by suitable adjustment of the brake asto prevent the tension set up in the stressed web and determined by thebraking efiect from being materially affected by the additional stressproduced in the web by the printing rollers.

What I claim is:

1. A process for printing on a transparent flexible foil consistingin-bringing the foil into a stretched and extended condition andsubjecting it to the printing operation while maintaining said stretchedcondition.

2. A process for printing on a transparent flexible foil by means of aplurality of printing elements consisting in introducing the web intoprinting position while keeping the printing elements out of operativeengagement with the web, exerting a pull on the web to bring it into astretched condition and bringing the printing elements into operativeengagement with the web and causing them to print upon the web whileniiaintaining the latter in said stretched condit on.

3. A process for printing on a transparent flexible foil by means of aplurality of printing elements consisting in introducing the web intoprinting position while keeping the printing elements out of operativeengagement with the web, exerting a pull on the web to bring it into astretched condition and bringing the printing elements into operativeengagement with the web and causing them to print upon the web whilemaintaining the latter in said stretched condition, the tension of theweb being larger than that at which any substantial additionalstretching could occur by the action of the printing elements on theweb.

4. A process for printing on a transparent flexible foil by means of aplurality of printing elements consisting in introducing the web intoprinting position while keeping the printing elements out of operativeengagement with the web, exerting a pull on the web to bring it into astretched condition approaching the limit of its elasticity and bringingthe printing elements into operative engagement with the web and causingthem to print upon the web while maintaining the latter in saidstretched condition.

5. A process for printing on a transparent flexible foil by means of aplurality of printing elements comprising introducing the web intoprinting position while keeping the printing elements out of operativeengagement with the web, subjecting the web to an advancing pull in thefeeding direction beyond the printing elements and to a braking actionin advance of the printing elements and exerting thereby a. pull on theweb to bring it into an elongated condition but within its elasticlimit, and bringing the printing elements into operative engagement withthe web and causing them to print upon the web while maintaining thelatter in the stretched condition.

6. In the operation of machines having printing couples for printing ona transparent flexible foil, the step which comprises subjecting thefoil to such a degree of tension during the printing operation as toproduce and maintain a strain in the foil which is many times largerthan that at which any substantial additional stretching could occur bythe action of the printing elements on the foil.

7. In the operation of machines for printing on a transparent flexiblefoil web and having a web reel, at least one printing unit and apositively driven pulling spindle, in tandem relationship, and a brakecooperating with said reel, the step which comprises applying said braketo a degree producing a pull on the web which brings it into a stretchedcondition approaching the limit of its elasticity.

8. In the operation of printing machines comprising a web reel carryinga supply roll of a transparent flexible foil web, at least one rotaryprinting couple, a pulling spindle adapted to pull said web from saidsupply reel through said printing couple, and a brake cooperating withsaid reel, the steps which comprise driving the pulling spindle and theprinting couple at the same peripheral speed and applying said brake toa degree producing a pull in the web which is many times larger thanthat at which any substantial additional stretching could occur by theaction of the printing elements on the web.

9. In the operation of printing machines comprising a web reel carryinga supply roll 01 a transparent flexible foil web, a plurality ofdifl'erent printing couples, a pulling spindle adapted to pull the webfrom said supply roller in succession through said printing couples,means

